In a conventional automatic transmission, a torque converter is typically included in the driveline. It is located between the crankshaft of an internal combustion engine and the transmission gearing that establishes torque flow paths to the vehicle wheels. The function of the torque converter is to provide fast and smooth vehicle launch via its torque multiplication and driveline torsional damping capabilities. Due to the nature of the fluid coupling in the torque converter, a certain amount of energy is lost in the fluid as the turbine slips with respect to the engine speed, which results in efficiency losses and a corresponding reduction in vehicle fuel economy. Starting clutch technology may provide a more fuel efficient device for vehicle launch as a replacement for the torque converter.
The fluid coupling of the torque converter is effective at preventing excitation of the vehicle driveline as a result of engine vibrations because the vibrations are dissipated in the torque converter fluid. However, if a starting clutch is used to replace the torque converter, then the starting clutch must be controlled to prevent such excitation of the vehicle driveline and to provide a vehicle launch which is as smooth as that of a torque converter equipped vehicle.
The absence of the torque converter also leaves the driveline with no damping during gear shifting. Consequently, the driveline may vibrate or “ring ” during the shift, which may cause objectionable torsional vibration on the vehicle.